1. Field of the Invention
The present invention relates to a solenoid actuator and, more particularly, to a solenoid actuator which may be suitably incorporated, for example, in a solenoid valve for use in automotive engines and engine accessories.
2. Description of the Prior Art
Solenoid actuators are widely used in various fields of industries. An example of application of the solenoid actuators includes solenoid valves which are used to control flow of fluids in accordance with varying electric signals.
As shown in FIGS. 1A and 1B of the accompanying drawings, a solenoid valve typically includes a solenoid coil 1 wound around a magnetic pole piece 2. An armature 3 as a movable member is arranged in alignment with the pole piece and is linked to an output rod 4 which is intended to control a valve section 5 shown only schematically.
The solenoid coil 1 is surrounded by a magnetic yoke member which operates to magnetically couple the pole piece 2 and the armature 3 with each other. In most instances, the yoke member is made of an outer casing 6 and a separate upper plate 7 which are assembled together by inwardly crimping the uppermost end 8 of the outer casing 6 as shown. As the solenoid coil 1 is energized, a path of magnetic flux will be formed across the yoke member, armature 3 and the pole piece 2 to attract the armature toward the pole piece.
In use, it has been customary to install the solenoid valve on a support housing by using bolts or screws. To this end, the solenoid valve is generally provided with a mounting bracket 9 by which the solenoid valve is bolted to the support housing 10. As a result, the solenoid valve as installed on the housing is generally exposed to the ambient atmosphere.
An essential designing requirement for a solenoid actuator is that the magnetic component parts thereof, such as yoke, pole piece and armature, which are intended to form the magnetic flux path must all be made of a ferromagnetic material such as iron and ferrous alloy.
One of the problems which must be overcome in designing a solenoid actuator which is durable and has a prolonged service life is that the ferromagnetic material which is used to fabricate the yoke, pole piece and armature is apt to rust.
Particularly, in automotive applications wherein the solenoid actuators and solenoid valves are mounted on automotive engines and engine accessories, the solenoid actuators are subjected to chemical attack by sodium chloride and calcium chloride which are spread on the road surface in the cold seasons as an antifreezing agent, so that the yoke, pole piece and armature of the solenoid actuators will be readily corroded.
Corrosion by the antifreezing agent is accelerated thermally because the automotive engine rooms are held at an elevated temperature ranging from 80.degree. C. to 120.degree. C. Furthermore, the solenoid coil evolves heat as it is energized so that the solenoid actuators are heated at a high temperature which may occasionally reach 150.degree. C.
As in this way the solenoid actuators are placed in extremely corrosive conditions, the yoke, pole piece and armature which are made of a ferromagnetic material would be readily corroded unless subjected beforehand to a high degree of rust prevention process such as plating. The bracket 9 and bolts must also be adequately plated to prevent premature rust formation.
High quality plating such as plating with nickel-zinc alloys and formation of a thick layer of plating is costly to perform and hinders reduction in the production costs.
Accordingly, it is an object of the present invention to provide a solenoid actuator having a design which is adapted to present a high degree of anti-corrosion property.
Another object of the invention to provide a solenoid actuator which is rust free and yet may be manufactured at limited production costs.
Another problem encountered with the conventional solenoid actuators is that a substantial labor is required during installation work because the mounting brackets must be carefully positioned and the bolts firmly fastened.
Accordingly, another object of the invention is to provide a solenoid actuator which is easy to install.
A still another object of the invention is to provide a solenoid actuator which is easy to assemble and easy to manufacture.